Field of the Invention
Aspects of the present invention relates to an image processing apparatus and an image processing method.
Description of the Related Art
Conventionally, processing using an optical character reader (OCR) has been performed as processing for detecting an orientation of a document image read by a scanner with respect to a normal direction.
Japanese Patent Application Laid-Open No. 2010-130634 describes an apparatus which determines, when a sensor device such as a scanner reads a document image, how the document image is inclined (skewed) with respect to the normal direction. The apparatus described in Japanese Patent Application Laid-Open No. 2010-130634 determines a skew angle of the document image (the read image) with respect to a registered image similar to the document image based on coordinates of feature points of the document image and coordinates of feature points of the registered image.
Japanese Patent Application Laid-Open No. 8-97980 describes an apparatus which corrects and resolves displacement in a document feeding direction (a sub-scanning direction) caused in a read image when a plurality of reading sensors (sensor devices) for reading a document is disposed with each inclination.
The apparatus described in Japanese Patent Application Laid-Open No. 2010-130634 can detect skew of a document (a skew angle of the document placed inclinedly) with respect to the sensor device. However, as a premise for that, the sensor device is to be accurately (vertically) placed with respect to a reading platen or a sheet passing path of the document. In other words, the apparatus described in Japanese Patent Application Laid-Open No. 2010-130634 cannot accurately detect the skew of the document with respect to the sensor device when the sensor device is not placed vertically to the sheet passing path of the document. The technique discussed in Japanese Patent Application Laid-Open No. 2010-130634 is a technique which is established on the premise that an assembling angle of the sensor device is maintained at a desired angle.
The apparatus described in Japanese Patent Application Laid-Open No. 8-97980 can correct the displacement in the sub-scanning direction, however, there is no teaching of correcting the assembling angle of the sensor device. In other words, the apparatus described in Japanese Patent Application Laid-Open No. 8-97980 cannot perfectly correct reading resolution in a main scanning direction. The assembling angle of the sensor device is corrected by rotation coordinate transformation, however, there is no description of the rotation coordinate transformation in Japanese Patent Application Laid-Open No. 8-97980. The apparatus described in Japanese Patent Application Laid-Open No. 8-97980 cannot correct the reading resolution in the main scanning direction and cannot obtain an accurate read image.
In the case of a large-sized scanner capable of reading a sheet exceeding an A3 sheet size, a plurality of sensor devices may be bonded with each other and used. Regarding the large-sized scanner, if linearity of the individual sensor device can be guaranteed, the fact that the plurality of the sensor devices is assembled perfectly in parallel and vertical to the sheet passing path of the document cannot be guaranteed in some cases. Especially, regarding the large-sized scanner, because of its large size, the assembling angle of the sensor device may be changed due to a secular change, an environmental temperature change, an installation condition such as sunshine, and a use condition. Therefore, even if the plurality of the sensor devices is assembled accurately to an angle (vertical) at the time of shipment from the factory, the assembling angle may be changed in the subsequent use. In such a case, an accurate read image cannot be obtained just by detecting the skew angle of the document. In order to obtain an accurate read image, an assembling angle of each of the plurality of the sensor devices in addition to detection of the skew angle of the document is detected.